1. Field of Invention
The present invention relates generally to an air intake system and more particularly to a trap for adsorbing hydrocarbons in the air intake system.
2. Related Technology
Due to laws requiring the reduction in the levels of hydrocarbons that vehicles may emit into the atmosphere, it is necessary for automotive designers to include systems in vehicles to control such emissions, even when the vehicle is not operating. Hydrocarbons remaining from engine reactions can leak out of the engine through the engine's air intake system. It is therefore desirable to reduce the levels of hydrocarbons released in this manner.
When the engine is not operating, a low-velocity airflow containing hydrocarbons leaks out of the engine, through the air intake system, and into the atmosphere. When the engine is operating, a high-velocity airflow enters the air intake system from the atmosphere and flushes the hydrocarbons remaining in the air intake system into the engine, where they are combusted. Therefore, it is beneficial to retain hydrocarbons contained in low-velocity airflow until high-velocity airflow flushes the hydrocarbons into the engine.
One device for retaining hydrocarbons from the air released through the engine's intake is a filter-like device having a hydrocarbon trapping element. Typically, the hydrocarbon trapping device is formed of monolithic carbon and is disposed in the air intake system of a motor vehicle. Therefore, when the engine is operating and the high-velocity airflow is flowing towards the engine, the hydrocarbon trapping device is considered to be upstream from the engine. The hydrocarbon trapping device operates by adsorbing hydrocarbons from the low-velocity airflow and purging the hydrocarbons with the high-velocity airflow.
One problem arising with hydrocarbon trapping devices, however, is that the devices may act as an obstruction to the air flowing to the engine, thus causing a pressure drop in the airflow to the engine. Therefore, in order to substantially reduce or prevent a drop in air pressure across the hydrocarbon trapping device, it is advantageous to increase the amount of air that can flow through the device.
Another problem associated with hydrocarbon trapping devices is that the adsorbing element can become saturated with hydrocarbons; substantially reducing or ceasing adsorption of hydrocarbons. Therefore, in order to effectively trap hydrocarbons and to substantially prevent saturation of the device, it is advantageous to increase the adsorption capacity of the hydrocarbon trapping device.
Yet another problem associated with hydrocarbon trapping devices is providing the devices with enough strength to sustain the structural integrity during operation of the vehicle.
Therefore, it is highly desirable to have a hydrocarbon trapping device that substantially prevents large airflow pressure drops across the device, that is able to adsorb a relatively large amount of hydrocarbons without becoming saturated, and that maintains a sufficient structural strength throughout the life of the device.